1. Field of the Invention
The present invention relates to a method of blending oil-soluble photographic additives into a hydrophilic colloid layer and, in particular, to a method of dispersing oil-soluble photographic additives into a hydrophilic colloid composition or into water.
2. Description of the Prior Art
In the manufacture of a photographic silver halide emulsion layer or other hydrophilic colloid coatings, one must often blend water-insoluble or sparingly soluble compounds (hereinafter referred to as "oil-soluble photographic additives") in such coatings. If may further be required that such additives which are insoluble in the hydrophilic colloid vehicle be uniformly dispersed in the form of extremely fine particles.
A typical color photographic light-sensitive material is based on a silver halide emulsion, though other types of materials are known using various other kinds of light-sensitive components. Such silver halide color photographic materials comprise principally a support, a red-sensitive silver halide emulsion layer, a green-sensitive silver halide emulsion layer and a blue-sensitive silver halide emulsion layer, each provided on said support. Various arrangements and constructions of silver halide color photographic materials may be employed for different types of imaging processes including, for example, diffusion transfer color photography and silver dye bleach color photography. Mixed grain photographic products and multilayer products are also known.
A number of recent advances in color photographic technology have been brought about by the use of oil-soluble photographic additives, which are dissolved in substantially water-insoluble, low-volatile organic solvents (for example, high boiling point organic solvents) and then dispersed into a hydrophilic colloid aqueous solution with the aid of an anionic surface active agent as an emulsifier. Such oil-soluble photographic additives include oil protected couplers, UV absorbing agents, fade preventing agents, antioxidants, dye precursors for color diffusion transfer, dye developers, etc.
Various methods are known for emulsifying and dispersing such oil-soluble photographic additives including methods disclosed in U.S. Pat. Nos. 2,739,888, 3,352,681, etc., for dispersing UV absorbing agents; the methods disclosed in U.S. Pat. Nos. 2,360,290, 2,728,659, 3,700,453, etc., for dispersing diffusion-resistant alkylhydroquinones used for preventing dye fogging, staining and color mixing.
Usually, anionic surfactants are used to disperse oil-soluble photographic additives. For example, the method set forth in U.S. Pat. No. 2,332,027 employs Gardinol WA (a sulfonated coconut fatty alcohol, Du Pont de Nemours & Co.) and triisopropylnaphthalenesulfonates. Japanese Pat. No. 428,191 discloses a method based on the use of water-soluble coupler containing a sulfonate or a carboxyl group together with a long-chain aliphatic group as an emulsifier. U.S. Pat. No. 3,676,141 describes a method relying upon a combination of an anionic surfactant containing a sulfonic group and a nonionic surfactant containing an anhydrohexyl ester unit.
In designing and fabricating a color photographic product, the light-sensitive coatings have finite thicknesses and the presence of incorporated additives in the form of coarse particles in the coatings can cause light scattering and deteriorate the transparency of the finished product. Furthermore, the image sharpness as well as the graininess of the photograph can be remarkably deteriorated. In contrast, when a coupler is dispersed in fine particles, the surface area per unit of weight of the coupler increases which in turn increases the rate and the efficiency of dye development, thus bringing about an improvement in the covering power of the resulting color image.
Accordingly, it is important that the growth of coarse particles during storage of an emulsified product be prevented. Emulsified products prepared by either of the methods cited above exhibit insufficient storage stability. In particular, when they were stored for an extended period of time at low temperatures, or for 24 hours at 40.degree. C., the growth of coarse particles is unavoidable.